This invention pertains to rejuvenation of particulate used catalysts removed from catalytic hydroprocessing of carbonaceous feedstocks. It pertains particularly to a catalyst rejuvenation process and apparatus utilizing only liquid/solid contact with a polar solvent and a dilute acid solution for substantial removal of contaminant metals and subsequent oxidation of essentially all carbon deposits from the used catalyst.
Various processes for rejuvenation of spent catalysts used in hydroprocessing of hydrocarbon feedstocks are known. For example, U.S. Pat. Nos. 4,454,240 and 4,595,666 to Ganguli each describe a procedure for spent catalyst regeneration by solvent washing and acid treatment steps, in which the spent catalyst is washed with naphtha or toluene solvent to remove retained heavy oil, heated to remove the retained solvent, water washed to fill the catalyst pores, then passed to an acid treatment vessel and contacted with a dilute acid solution. The acid-treated catalyst is washed with water to remove the retained acid, and then dried and oxidized at desired high temperature to burn off carbon deposits. However, for these catalyst regeneration processes, separate vessels are needed for washing the used catalyst with the solvent and for treating the catalyst with the acid, so that movement of the catalyst from the solvent washing vessel to the acid treating vessel results in appreciable attrition of the catalyst and undesired handling costs. Also, the catalyst washing vessel must be constructed to achieve efficient liquid/solid contacting for process oil removal, and for gas/solid contacting for solvent removal and drying of the catalyst. U.S. Pat. No. 4,720,473 to Welch et al discloses stripping used catalyst to remove oily residue, grading the catalyst for size, and then oxidizing it to remove coke deposits. Also, U.S. Pat. Nos. 4,769,219 and 4,863,884 to Tasker et al disclose a vessel assembly and method steps for rejuvenating used catalyst in a single vessel, utilizing successive solvent washing, vacuum drying, acid treatment and gas drying steps. Thus, although some catalyst rejuvenation procedures for used hydroprocessing catalysts are known, these procedures have various disadvantages and further cost effective improvements in catalyst rejuvenation processes for such used catalysts are needed in the industry.